The present invention relates to an interface device and an image forming apparatus. More particularly this invention relates, an interface which executes signal processing to image data transmitted from an external device and transmitting the data to a printer.
In recent years, digital copier with an external device connected thereto, in addition to an ordinary use as a copier for receiving image data sent from the external device and outputting an image of the data It is needless to say that this copier also has all the functions provided in an ordinary copier.
For example, a printer controller and a FAX controller are used as an external device. When a FAX controller is connected to a digital copier, data with a resolution of 100 dpi to 400 dpi is sometimes transmitted from the FAX controller, or data with different resolution in main and auxiliary scanning directions is also sometimes transmitted therefrom.
When a printer controller is connected as an external device, data with a different resolution may be received in order to connect it to a plurality types of controller (in a case, for instance, where a digital copier is required to be compatible with an old type of controller).
As a conventional technology for supporting data with different resolutions, for instance, an image processor is disclosed in Japanese Patent Laid-Open Publication No. HEI 5-183697. In this image processor, a printer engine is connected to a printer controller for forming a visible image by using a rotatably driven drum. A PCPU first receives one of a plurality of different resolutions (300 dpi, 600 dpi) from the printer controller via a connection cable or from a switch circuit via a data line. Then the PCPU checks the resolution and sets the speed of the drum in such a manner that the speed will be xc2xd in case of 300 dpi as compared to the 600 dpi. The PCPU then performs smoothing processing corresponding to the determined resolutions according to a prespecified algorithm. Namely, this image processor allows an image in high recording density to be output without using a high-speed device by varying a linear speed of a photoconductive drum according to recording density of the external device.
However, the above mentioned image processor has difficulty in matching conditions of image formation with a plurality of linear-speed conditions because an image-formation speed of a printer section is changed, and has a problem of generating degradation in image quality especially in a case of a color engine.
This invention has been made in the light of the problems described above. It is an object of the present invention to provide an interface device and an image forming apparatus which allow image data with various resolutions sent from an external device to be printed with high quality without any change in an image-formation speed of its printer section.
In the interface device of this invention, a line-synchronizing signal thinning unit thins out a line-synchronizing signal transmitted from a printer section at a prespecified cycle according to set resolution and transmits the signal to an external device as a thinned line-synchronizing signal, a resolution setting unit sets resolution of image data, a storing unit stores therein image data transmitted from the external device at a cycle of the thinned line-synchronizing signal, a data converting unit repeatedly reads out an identical line and/or an identical pixel of the image data stored in the storing unit according to the set resolution and transmits the read out data to the printer section. Therefore, when image data with a different resolution from that of the printer section is transmitted from an external device, the need for changing the image-formation speed of the printer section is eliminated.
Other objects and features of this invention will become apparent from the following description with reference to the accompanying drawings.